Telephone system



Oct. 20, 1936. .1 H. Voss TELEPHONE SYSTEM 62m UU IJHHMM HH-- -I il-..Al--. -i U@ .-b |16 N2 nai, W .41 LN. www n H1@ Nlulllnmom 2 all? Oct.20, 1936. .1. H. Voss TELEPHONE SYSTEM Filed July 5, 1935 4 Sheets-Sheet2 Oow INVENTOR.

JOHN H. VOSS OmOO w2 mmh-LO A TTORNEY.

Oct. 20, 1936. J. H. Voss TELEPHONE SYSTEM Filed July 5, 1935 4Sheets-Sheet 3 A TTORNE Y.

Oct. 20, 1936. J. H. Voss TELEPHONE SYSTEM Filed July 5, 1955 4Sheets-Sheet 4 A TTORNEY,

Patented Oct. 20, A1936 UNITED' STATES PATENT oFFlcE TELEPHONE SYSTEMApplication July 5, 1935, Serial No. 29,863

14 Claims.

This invention relates to' telephone systems.

It is concerned particularly with telephone systems including a mainexchange and a private branch exchange in which the local calls andcalls outgoing from branch exchange subscribers are handled throughautomatic switches, while calls incoming to the branch exchange areintercepted and completed under the control of an attendant operator.The main object of the invention is concerned with the production of newand improved features of operation which enable the inter-exchangeservice to be handled more satisfactorily by means of a minimum ofrelatively simple equipment. j l5 GENERAL DESCRIPTION As is well known,local service ina private automatic branch exchange is handled throughdial-controlled automatic switches; calls from branch exchange lines tothe main exchange are handled over inter-exchange trunk lines Seized bythe automatic switching apparatus in the branch exchange responsive tothe dialling of the main-exchange designation; while calls incoming fromthe main exchange to the branch exchange are intercepted by the branchexchange operator, who directs them to the appropriate or desired branchexchange lines.

From the standpoint of handling incoming calls, attended privateautomatic branch exchanges may be divided into two classes: (l) privateautomatic branch exchanges in which the incoming calls are completedthrough automatic switching apparatus controlled by the 3branch-exchange attendant or operator, and (2) private automatic branchexchanges in which incoming calls are extended manually through a manualswitchboard presided over by the branch exchange operator. The presentdis- 40 closure has to do with a private automatic branch exchange ofthe Second of the above-mentioned classes.

The private automatic branch exchange disclosed herein containsdesirable features, including the following:

1. In order to insure the secrecy of conversation against accidental orintentional invasion or eavesdropping by the branch-exchange operator,arrangements are provided such that a 50 warning tone-signal istransmitted over a connection established through the operatorsswitchboard in the event that the operator throws the talking key of acord circuit overwhich a conversation is taking place, this ar- 55rangement being controlled through the answering supervisory relay andcontacts of the associated talking key.

2. In order to prevent the operator from plugging in to themanual-switchboard multiple of the local subscribers line andoverbearing a con- 5 versation in progress, and also to prevent theoperator from inadvertently interfering with a dialling operation inprogress in the event that she makes connection with a busy local line,the tip and ring conductors of the local plug of each 10 of the cordcircuits are maintained normally disconnected from the main part of thecord circuit, and the connecting up of the normally disconnected talkingconductors is made dependent upon the operation of an idle-test relayover the sleeve conductor of an idle subscribers line. By thisarrangement,the operator may insert her plug in the jack of a busy lineand still be unable to hear the conversation over the line and beprevented from interfering with the progress of a 2 partially completedconnection, because the tip and ring strands of the local plug of thecord circuit are maintained open.

3. In order to prevent the operator from defeating the arrangement setforth in the preceding paragraph by employing the trunk plug of a cordto listen in on a busy connection, contacts controlled jointly by thesleeve-connected trunk supervisory relay and the talking key of the cordcircuit bring about the transmission of the aforementioned warningtone-signal to the operators headset conductors and thus to the linebeing intruded upon thereby notifying the operator that her intendedintrusion is not going unnoticed, and notifying the two Subscribers ofthe busy connection that the secrecy of their conversation is beinginvaded.

4. In order to provide for the making of a more reliable busy testthrough the bringing of the tip and the plug into engagement with thesleeve of the jack, circuit arrangements have been provided to respondto the operation of a busy-test relay (over the tip of the plug fromguarding potential encountered on the sleeve of the jack of a busy line)to bring about the application of a tone signal to the operators headsetconductors. By this simple provision, the operator need only make surethat the tip of plug makes rm contact with the sleeve of the jack. Underthis condition, the absence of a tone signal in the operators receiverindicates that the line is idle. This same arrangement operates inconjunction with a previously mentioned feature to secure correctperformance in the event that the operator inadvertently orintentionally fails to make the tip-sleeve busy test and inserts theplug into the jack of a busy line. The above busytest relay thenoperates over the tip conductor of the busy line to cause theapplication of a busy-tone signal to the operators headset conductors,while the tip and ring conductors of the plug are maintaineddisconnected from talking conductors of the cord because of the absenceof an idle-indicating potential on the sleeve element of the jack. Thebusy-test relay is preferably of high impedance, so that its connectionto the tip contact of a jack will not interfere with the progress of aconnection being set up automatically under the control of a dial. f

5. In order to provide the branch exchange `operator with a ready meansof making connecbranch exchange has CII tion with bus'y branch-exchangelines for'the purpose of offering incoming calls, an offering cord andplug are attached to the operators headset conductors, through which theoperator may extend connection to any local line multipled into themanual switchboard. But, the above mentioned warning tone-signalarrangement is associated also with the offering cord so that theinsertion of the offering cord into the jack of the local line resultsin the application of warning tone-current to the operators headsetconductors and to the conductors ofthe local line connected with so asto warn the subscribers that the operator is telephonically connectedwith the connection.

6. In order to enable a local subscriber engaged in an inter-exchangeconversation to obtain additional information, for example, each of theinter-exchange trunk lines terminating at the a branch connectionextending to the automatic switchboard, together with switching meanscontrollable at will over a localline to switch the local linetemporarily into connection with the automatic switchboard so that thesubscriber may set up a local connection automatically to another localline and then later switch the connection back to the inter-exchangetrunk line.

7. An additional desirable feature is found in the arrangementcontrolled partly through a local cord and partly from an inter-exchangetrunk circuit for disconnecting both plugs of a local cord when thelocal subscriber involved in a call incoming from the main exchangereplaces his receiver, thereby freeing the branch-exchange end of thetrunk line immediately as well as immediately freeing the local line forfurther use, pending the taking down of the local cord by the branchexchange operator.

8. In order to render completely eiective the aforementioned arrangementfor preventing the operator from either eavesdropping or interferingunintentionally with the progress of calls being set up automaticallyfrom local substations, a cut-oir relay has been added to each of thetwo-way inter-exchange trunk lines, which relay operates when thetwo-way trunk line is seized automatically in the branch exchange to cutoff the switchboard extension of the trunk line so that thecorresponding jack at the operators switchboard is telephonicallydisconnected.

Description of drawings Referring now to the accompanying drawings,comprising Figs. 1 Yto 4, they show by means of the usual circuitdiagrams a suicient amount of the equipment involved in a telephonesystem embodying the invention to enable the invention to beunderst0od.`

as the cord circuit CC, Fig. 1), together with l the offering cord whichterminates in the offering vplug OP;

Fig. 3 shows the one-way outgoing trunk line TI and the associated trunkcircuit TCI; and

Fig. 4 shows the two-way interexchange trunk line T2 and associatedtrunk circuit TC2.

In Fig. 1, the lines from the automatic substations A and B extend asindicated to the line switches LSZ and LSI, respectively. These lineswitches may be of any desired construction, being indicated onlydiagrammatically in the drawings, as are the similar line switches LS3and LSI.

The line switches LSILS4 have common access to selectors, of which theselector SI is one. The selector SI may be of the usual Vertical androtary type, having its back contacts arranged in horizontal rows orlevels. The selector SI has access by way of one of its levels of bankcontacts to the connector CI, which is one of a group of connectorsthrough which connection may be extended to the 10U-line groupcontaining the line of substation B. On another of its levels, theselector SI has access to the trunk lines of Figs. 3 and 4. The one-Waytrlmk line of Fig. 3 is indicated as being a first-choice trunk line,while the two-way trunk line of Fig. 4 is indicated as being taken intouse only after the first-choice trunk lines have been tested and foundto be busy. This is inaccordance with the usual practice of reservingthe more expensive two-way trunk lines until all of the less expensiveone-way trunk lines have been taken for use.

It is to be noted that the line jack LJ I is a manual-switchboardmultiple of the called multiple of the line of substation A at theautomatic switchboard, while the line jack LJ2 is a similar multiple ofthe called multiple of the line of substation B. It will be notedfurther that the trunk jack TJ is a manual-switchboard extension of thetrunk T2, Fig. 4, by way of the trunk circuit TG2, and that the lineswitches LS3 and LS4 are associated respectively with the trunk circuitsTCI and TC2. It may be mentioned at this point that it is through lineswitches such as LS3 and LS4 that transfer service is made available tolocal subscribers involved in inter-exchange conversation, as will bepointed out more in detail hereinafter.

At the cord circuit CC, Fig. 1, the trunk plug 'I'P is the one designedto be inserted into trunk jacks such as TJ, while the local plug LP isthe one to be inserted into a local jack, or line jack, such as LJ I andLJ2. The cable 200 is a multiple cable which multiples the commonconductors 22I230l (associated with the position equipment of Fig. 2)with the various cord circuits, of which the cord circuit CC, Fig. 1, isone.

Detail description The disclosure havingbeen described generally, adetailed description of the operations involved in setting up andhandling the several kinds of connections will now be given. For thispurpose it will be assumed rst that the subscriber at subchangesubscriber, removes his receiver and dials the designation of the mainexchange.

Outgoing call over a one-way trunk When the receiver (not shown) isremoved at substation A, the line switch LS2 operates in the usualmanner to select an idle selector, the' selector SI, for example. Uponthe seizure of the selector SI the automatic switchboard equipment is inreadiness for the subscriber at substation A to dial the designation ofthe main exchange.

When the designation of the main exchange (the digit 0, for instance) isdialled, the selector SI raises its wipers opposite the level of bankcontacts containing the main-exchange trunk lines, whereupon the wipersare rotated over the bank contacts in search of an idle trunk line.Under the assumption that the trunk line TI, Fig. 2, is idle, the wipersof the selectors SI come to rest on the bank contacts from which theconductors 309, 3I0, and 3II extend to the trunk circuit TCI, associatedwith the trunk line TI,

Fig. 3.

Upon the seizure of the trunk circuit TCI, line relay 304 thereof, whichis connected to conductors 309 and 3I0 through the right-hand windingsof repeating coil 303 and the windings of the differentialtransfer-control relay 308, energizes over the line of substation A.Upon energizing, line relay 304 places a bridge across the conductors ofthe trunk line TI at its upper contacts through the left-hand windingsof repeating coil 303 and the resistor 3I5, which is shunted around thetalking condenser associated with the lefthand repeating-coil windings.The closure of this bridge prepares automatic switching apparatus in themain exchange for further dialling operations in the event that the mainexchange is an automatic exchange, while, if instead the main exchangeis a manual exchange, the bridging of the trunk line TI results in thelighting of the usual line lamp at the operators switchboard.

As a further result of its energization, line relay 304 closes a circuitfor release relay 306 at its inner armature, whereupon relay 306operates and prepares a locking circuit for transfer relay 305 at itslower armature, at the same time applying a holding potential toconductor 3II at its upper armature. The holding potential thus appliedto conductor 3H is effective to maintain the selector SI and the lineswitch LS2, Fig. 1, operated until the receiver is replaced at thecalling substation A.

When the connection over the trunk line TI has been set up through themain exchange switchboard to the desired line and an answer has beensecured, conversation may take place between the line of substation Aand the called line through the line switch LS2, the selector SI, thetrunk circuit TCI, and the trunk line TI.

When the conversation is finished, the subscriber at substation Areplaces his receiver, whereupon line relay 304 restores and opens thebridge across the conductors of the trunk TI at its upper contacts,thereby bringing about the release of the automatic switching equipmentin the main exchange in the event that the main exchange is an automaticexchange, or bringing about the lighting of the usual disconnect lamp atthe manual switchboard in the main exchange, provided the main exchangeis a manual exchange.

The deenergization of line relay 304 brings about the deenergization ofrelay 306, whereupon holding potential is removed from'conductor 3| I,permitting the release ot the selector SI and line switch LS2 to takeplace.

Transfer service through the one-way tmnk circuit TCI Let us assume nowthat the subscriber at substation A has set up an outgoing connection byway of the lineswitch LSI and the selector SI over the trunk circuit TCIand the trunk TI, and

that during the conversation the subscriber at substation A desires toconverse momentarily with another local branch exchange subscriber, toobtain additional information, for example. For this purpose, thesubscriber at substation A after requesting the main exchange subscriberto hold the line for a moment, momentarily depresses his groundingtransfer-control push button PI, thereby applying ground potentialmomentarily to one of the conductors of his line. .This momentaryapplication of ground potential to a conductor of the line of substationA unbalances the current-flow through the two windings of thedifferential transfer-control relay 308 suiciently to cause an operationof relay 300. Upon operating, relay 308 closes a circuit for theinefficient upper Winding of the two-step transfer relay 305, whereuponrelay 305 energizes just suflciently to close its lightly adjustedfirst-step contacts, the inner lower contacts of the relay. Theactuation of these contacts closes a locking circuit for both windingsof relay 305 in series, through contacts controlled by the armature ofunlock relay 301 and the lower contacts of 'release relay 30G. Nocurrent, however, flows through the lower winding of relay 305 for thetime being because the initial circuit for the upper winding of relay305 is an effective shunt around the lower winding of the relay.

When the push-button PI is released, transfercontrol relay 308 restoresresponsive to the restoration of the normal balanced condition ofcurrent flow through its windings. The initial circuit for the lowerwinding of relay 305 is thereby opened, whereupon the locking circuitfor both windings of the relay in series becomes effective, and relay305 operates fully to seize the lineswitch LS3, Fig. l, by way ofconductors 3I2-3 I 4. At its upper armature, transfer relay 305 places ashunt around the upper contacts of the line relay 304 so as to maintainthe trunk line TI continuously bridged, and at its lower armature itshifts the contacts of transfer control relay 308 from its own windingto the winding of unlock relay 301.

The line switch LS3 operates over the calling line (A) and overconductors 3I2 and 3I3 in the usual manner to select an idle selector,similar to the selector SI. Ground potential is placed on conductor 3I4of the line switch LS3 by the seized selector to close a holding circuitover conductor 3I4 and through the inner upper contacts of transferrelay 305 for release relay 306, thereby maintaining this relay operatedafter line relay 304 has fallen back, which it does upon being dis-vconnected at the transfer contacts of relay 305.

The subscriber at substation A now proceeds to dial the number of thedesired local line, whereupon the connection is extended through theautomatic switchboard to the desired line and called local'subscriber,he again momentarily depresses the'push button PI, again bringing aboutture to the locking circuit of transfer relay 305,

at the same time disconnecting the locking circuit of transfer relay 305from ground potential at the lower contacts of release relay 306. Then,when transfer-control relay 308 restoresV (when PI is released). itopens the circuit of relay 301 and the locking circuit of relay 301.Relay 305, being slow-acting, remains operated for a short intervalafter the circuit is opened, so that transfer relay 305 is permitted tofall back and open a point in its locking circuit before relay 301restores.

Upon restoring, transfer relay 305 disconnects conductors 3|2, 3|3, and3|4, permitting the con- 'nection set up through the lineswitch LS3 toclear out.

Line relay 304 now operates again over the line of substation A andagain takes over the control of release relay 306 and the control overthe bridge established across the outgoing trunk line TI. A momentlater, the slow-releasing unlock relay 301 restores. Relay 301, it isnoted, maintains the trunk line TI bridged during the transition periodfollowing the restoration of relay `305 and the resulting reoperation ofline relay 304.

The interrupted conversation between the subscriber at substation A andthe main exchange subscriber reached over the outgoing trunk line .Tlmay now be resumed.

It will be appreciated, of course, that the subscriber at substation Amay, if he so desires, again interrupt the conversation with the mainexchange subscriber and again transfer his connection over to the lineswitch LS3 for the purpose of setting up another local inquiryconnection in the manner described hereinbefore.

When the conversation is completed the subscriber at substation Areplaces his receiver, whereupon the interexchange connection is clearedout as before explained.

An outgoing call over a two-way trunk For the purpose of explaining theoperation of the trunk circuit TC2, Fig. 4, when it is seized in thebranch exchange in an outgoing call, it will be assumed that thesubscriber at substation A makes an outgoing call by way of the selectorSl, for example, at a time when all of the one-way trunk lines, such asthe one shown in Fig. 3, are in use and that the trunk line T2, Fig. 4is the rst one found to be idle by the selector SI as it rotates overthe trunk-line contacts. That being the case, the trunk circuit TC2,Fig. 4, is seized by the selector SI over conductors 42l-423, whereuponline relay 404 of the trunk circuitTCZ energizes over the line ofsubstation A and over conductors 42| and 422. At its upper contacts,line relay 404 bridges the conductors of the trunk line T2 through theleft-hand windings of repeating coil 403 and resistor 4|3, while at itslower armature it closes a circuit for release relay 405. Release relay405 thereupon operates and places ground potential on conductor 423 atits upper armature, thereby providing a holding circuit for the selectorSI and the line switch LS2. Release relay 405 also disconnects thering-up relay 405 from in bridge of the conductors of the trunk line T2,while at its inner upper'armature it prepares a locking circuit fortransfer relay 4|0.

At the lower armature of release relay 405, a. circuit is closed over421 for busy lamp |23 to notify the operator that the trunk is in use.

Jack-cut-off relay 4|2, whose lower winding is normally in series withconductor 42|, energizes over conductor 42| and over the calling line,`in series with line relay 404. Upon energizing, relay 4|2 closes alocking circuit for its upper Winding to the grounded release while atits upper and lower armatures it disconnects conductors 424 and 425which lead to the trunk jack TJ. The trunk jack TJ is therefore nolonger in multiple of the trunk circuit TC2, and will be maintaineddisconnected for the duration of the call.

The lower Winding of jack-cut-oi relay 4| 2 is by-passed at the lowerarmature of the relay, so as to alord a better talking and diallingcircuit.

The desired connection is completed in the main exchange, eithermanually or responsive to further dialling on the part of the subscriberat substation A, depending upon whether the main exchange is a manualexchange or an automatic exchange. In the event that the main exchangeis an automatic exchange, the dialling impulses are repeated by linerelay 404 at its upper contacts, as in the case of line relay 304 oftrunk circuit TCI, Fig. 3.

Transfer service through the two-way trunk Circuit TCZ trunk conductor423,'

is to be noted that the transfer connection in this case is overconductors 4|3-4 5 to the line switch LS4, Fig. 1.

It is to be noted further that relays 409 and 4 I0 cooperate at theirupper contacts to maintain the trunk T2 bridged during the time theconnection is transferred away from the trunk T2 and pending thereoperation of line relay 404.

When the receiver is replaced at substation A at the end of theinter-exchange conversation, line and release relays 404 and 405restore, whereupon the removal of ground potential from conductor 423 atthe upper contacts of release relay 405 results in the clearing out ofthe automatic switches LSZ and SI.

Handling an incoming call For the purpose of `describing how incomingcalls are handled, it will be assumed that the trunk line T2, Fig. 4, isseized in the main exchange in a call for a subscriber of the branchexchange.

When the trunk line T2 is seized in the main exchange, ringing currentis projected thereover in the usual manner, operating ring-up relay 406which is bridged across the conductors of the trunk line T2 lthrough theassociated condenser. Relay 406 closes a circuit for call relay 401,which relay responds and closes a locking circuit at its inner upperarmature through contacts of release relay 405. Call relay 401 alsoprepares a circuit for hold relay 408 at its inner lower armature, whileat its upper armature it places ground po- 'tential on conductor 423 soas to mark the trunk line engaged immediately at the selectors such asSl Fig. 1.

Relay 401, at its inner lower armature, closes a circuit over conductor421 for busy lamp |23 at the trunk jack TJ, while at its lower armatureit closes a circuit over conductor 428 for the call lamp |24, therebynotifying the operator that a call has been received from the mainexchange.

The branch exchange operator responds to the lighted condition of thecall lamp |24 by inserting the trunk plug of a cord circuit, trunk plugTP of cord circuit CC, for example, into the trunk jack TJ.

When the trunk plug TP is inserted into the jack TJ, the strands of thecord circuit CC are bridged across conductors 424 and 425 operating theline relay 404 in the trunk circuit TC2 over the supervisory bridge inthe cord circuit CC, which bridge includes contacts controlled by thelower armature of connecting relay |06, contacts of the answeringsupervisory relay |05, and resistor |4. Upon operating through the cordcircuit CC, line relay 404 at its lower armature removes groundpotential from sleeve conductor 426 of the trunk jack TJ, therebypreventing false operation of the supervisory and release timer relay|08 in the cord circuit CC. Line relay 404 also closes a direct currentbridge across the conductors of the trunk T2 at its upper contacts,thereby causing the ringing condition to be terminated in the mainexchange and giving answering supervision.

Hold relay 408 operates through the lower contacts of the operatedrelays 404 and 401 to bridge the trunk line T2 at its upper contactsindependent of the upper contacts of line relay 404.

Release relay 405 responds to the operation of line relay 404 anddisconnects ring-up relay 406 at its inner lower armature; makes anadditional application of ground potential to conductor 421 at its lowerarmature; makes an additional application of ground potential to releasetrunk conductor 423 at its upper armature; and at its inner upperarmature it opens the locking circuit of call relay 401, at the sametime closing a locking circuit for the upper winding'of the operatedhold relay `408 and preparing a locking circuit for transfer relay 4|0.Relay 408 is therefore maintained operated throughout the remaining timeof the incoming connection under the control of release relay 405 so asto maintain the state of answered supervision over the trunk line T2 atits upper contacts. Y Upon-the falling back of call relay 401, the calllamp |24 at the trunk jack TJ is extinguished at the lower contacts ofthe relay, but conductors 423 and 421 remain grounded at contact ofrelease relay 405, thereby maintaining the trunk circuit TC2 guarded atthe automatic switchboard and maintaining busy lamp |23 lighted at thetrunk jack TJ.

In order to converse with the calling subscriber, the operator nowthrows her key Kl of the cord circuit CC into talking position, therebyoperating the right-hand contacts of the key. The tone lead 225 isconnected up at the upper contacts or' the talking key; the hold lead222 is connected up at the lower contacts of the talking key, While atthe middle contacts of the talking key the test lead 22| is brought intoconnection with the lower winding of connect relay |06. The testconductor 22| is normally grounded at the upper contacts of guardv relay20|. Assuming guard relay 20| to be in normal position at this time, theupper winding of connect relay |06 of the cord circuit CC is energizedover conductor test 22|, whereupon connect relay |06 operates and closesa holding circuit for its lower winding at its inner lower contacts,through the lower contacts of the talking key, and over hold conductor222 in series with guard relay 20|, Fig. 2. Guard relay 20| thereuponoperates in series with the lower winding of connecting relay |06 andremoves ground potential at its upper contacts from test conductor 22|to insure that no further connect relay such as |06, Fig. 1, is operateduntil the operator restores the key KI and permits connect relay |06 andguard relay 20| to restore.

As further results of its operation, connect relay |00 connects the tipand ring conductors 223 and 224 of position equipment PE with thecorresponding conductors'of the cord circuit CC; it connects thebusy-test lead 221 to the tip of the local plug LP; it connects thesplit conductor 228 to split relay |01 of the cord circuit; and itconnects the ring-start lead 226 to ring-start relay |04. At thenormally closed contacts controlled by the lower armature of relay |06,the bridge across the strands of the cord circuit CC by way of resistor||4 is opened, and the strands on the cord are now bridged only by thecommon tip and ring conductors 223 and 224, contacts of feed relay 203,secondary windings of the induction coil IC. and the articial line AL.The line relay 404 of the trunk circuit TC2 is held operated for thetime being through the bridge just traced.

The operator may now converse with the calling main-exchange subscriberover the cord circuit CC and the trunk line T2 and ascertain with whomconnection is desired.

It is to be noted that the operators receiver R, instead of beingdirectly associated with the secondary windings of the induction coil C(in the usual anti-sidetone arrangement involving the artificial lineAL), is replaced in this circuit by the primary windingof repeating coilRC, whose secondary winding leads to the receiver R. The primary windingof the repeating coil RC is shunted by a full-wave dry-disc rectifier2|0, which is so proportioned with respect to the voltages normallyapplied to it during conversation that it acts as a high-resistanceshunt normally, but acts as a low resistance shunt in the event of themomentary application of a high voltage surge. The operator is thusprotected in a large measure from loud, disagreeable noises which areotherwise produced occasionally in her receiver.

It may be pointed out that the transmitter T obtains its energizingcurrent from the condenser-shunted retard coil 209, and is in circuitwith the primary winding of the induction coil Assuming that theoperator learns that the calling subscriber desires to be connected withthe subscriber at substation B, accessible by way of the line jack LJ2,the operator may follow either of two procedures, depending upon theoperating instructions which she has received:

(l) She may forego the usual voluntary busy test and insert the localplug LP straightway into the line jack LJ2 of the line of the subscriberat substation B; or

(2) She may first make a busy test by touching the tip of the local plugLP to the sleeve of the line jack LJ2.

Testing the called Zine It is to be noted that busy-test relay 206 hasone terminal thereof connected to the negative or grounded pole of theexchange battery, While y heard by the calling subscriber.

the other terminal thereof is connected by way of busy-test conductor221, contacts of the operated connect relay |06, and contacts ofswitching relay |02, to the tip of the local plug LP of the cord circuitCC. In the event that the operator is instruceted to make a tipbusy-test, she places the tip of the plug LP in contact with the exposedportion of the sleeve of the line jack LJ2. In the event that the' lineof substation B is idle at this time the test or sleeve conductor |2|thereof has a negative potential thereon, through the usual cut-offrelay (not shown), and busy-test relay 206 therefore does not operate.On the other hand, if the line of substation B is engaged, there is aground potential on sleeve conductor |2| thereof with the result thatbusytest relay 206 operates over sleeve conductor l2 I. At its innercontacts, relay 206 closes a circuit for the ticker relay 205, while atits lower armature it places a shunt around the resistor 201 so as toincrease the amplitude of the signalling tone at this time. When ticketrelay 205 operates (in series with resistor 2| I), it closes a shuntaround its winding at its inner armature, which brings about adeenergization of the relay. Relay 205 therefore operates somewhat afterthe fashion of a buzzer, but less rapidly because its operation isdelayed by the lpresence of .the copper collar around the armature endof its core and the indicated copper sleeve over the entire part of thecore beneath the Winding, while its restoration vis further delayed bythe retarding eiect of its winding when short circuited at the innerlower contacts of the relay.

The intermittent operation of relay 205 while its circuit is maintainedclosed at the inner lower contacts of busy test relay 206, results inthe intermittent closure of a circuit at the lower contact of relay 205through the lower contacts of relay 206 and resistor 208 for thetertiary Winding of the induction coil IC. The current-flow induced inthe secondary winding of the induction coil IC by this intermittentclosure of the circuit through the tertiary Winding of the coil, resultsin the application of a tone signal to the operators receiver, whichtone signal may also be This tone signal is interpreted as an indicationthat the line of substation C is in use.

When the tip of the plug LP is removed from the sleeve of the jack LJ2,busy test relay 206 restores and terminates the intermittent operationof the ticker relay 205.

Assume now'that the operator is instructed to LJ2 without previouslydetermining Whether the connected line is busy or idle. Nevertheless,the operator does not establish a telephonic connection with the line(when it is busy), for the tip and ring strands of the plug LP are openat contacts of switching relay |02, and the controlling, idle-test relayhaving its lower terminal connected to ground through contacts ofcut-off relay |09, requires an idle-indicating potential on the sleeveconductor |2| of the jack LJ 2 for its operation. Therefore, busy-testrelay 206 remains connected to the tip of the plug LP. Since the line ofsubstation B is in use at this time, the potential applied to either ofthe talking conductors thereof is somewhere between the potentialsexisting at the two poles of the exchange battery (due to the bridgedcondition of the line and the potential l jack LJ2, the operator is dropin the usual battery-feed bridge (not shown) As a result, busy-testrelay 206 is operated over the tip of the line jack LJ 2 and causes thebusy tone to be applied by bringing about an operation of ticker relay205, as above described. The operator is therefore notified that theline of substation B is in use and that she should remove the plug LPfrom the jack LJ 2.

It may be pointed out at this time that the impedance of the busy testrelay 206 is made very high with respect .to the impedances normallyobtaining in connection with subscribers lines, whereby a diallingoperation, if occurring at this time over the busy line, is notinterfered with, and the automatic switching mechanism being operatedcontinues to operate without interference.

When the plug LP is withdrawn from the jack LJ2, busy test relay 206restores and ticker relay 205 ceases to operate.

Oering an incoming call to a busy line In the event that the operatordesires to make a talking connection with the line of substation B andinquire of the subscriber at substation B whether or not he cares toabandon the local connection in which is engaged and accept the incomingcall, the operator restores her talking key KI of the cord circuit ingplug OP to make connection with the desired busy line through the linejack LJ 2.

When the talking key KI is, restored, connecting relay |06 restores andreestablishes the supervisory bridge through resistor I 4. The guardrelay 20| in the position equipment PE, which has also maintained thetalking conductors of the offering plug OP disconnected, restores andreconnects these conductors to the operators headset conductors.

When the offering plug OP is inserted into the placed in telephoniccommunication with the line of substation B through the tip and ringconductors of the plug OP and the corresponding conductors of the linejack LJ 2. The lower winding of tone relay 202 is energized at this timeover the grounded sleeve conductor |2| of the line jack LJ 2 to operatethe ticker relay 205 and thereby apply the tone signal to the operatorsreceiver and to the operators headset conductors, thereby warning thesubscriber at substation B immediately that his conversation may now beheard by the branch-exchange operator. 'Ihe tone produced at this timeby the above described operation of ticker relay 205, althoughnoticeable, is suiiiciently mild that conversation is not materiallyinterfered with. Therefore, the branch exchange operator can nowconverse with the subscriber at substation B and inform him that she isholding an incoming call for him.

In the event that the two local subscribers to the conversation replacetheir receivers and the operator withdraws the offering plug OP from thelocal jack LJ2, tone relay 202 restores and ticker relay 205 ceasesoperating when vthe offering plug OP is removed from the jack PJ.Moreover, the line of substation B is freed and brought to its normalidle condition responsive to the receivers being replaced at substationB and the other substation included in the previously establishedconnection.

The. operator now inserts the local plug LP of the card CC into trunkjack TJ, whereupon idletest relay |0| is operated over Athe sleeve ofthe jack LJ2, conductor |2|, and the usual cut-of! CC and employs theolerrelay (not shown) to the negative pole of the exchange battery. Theline of substation B is caused to test busy to the automatic .switcheshaving access to it by the ground potential applied thereto through thewinding of idle test relay |I. Relay |0| operates switching relay |02 toclose the talking circuit to the line of substation B and to disconnectthe busy test conductor from the tip conductor of the plug LP. Switchingrelay |02 also closes a lighting circuit through contacts of .answeringsupervisory relay for supervisory lamp |26, while at its inner upperarmature rt 'prepares a circuit by way of contacts of relay |08 forcut-off relay |09.

The operator now operates thetalking key Kl again, again operatingconnect relay |06 along with guard relay 20|, thereby again associatingthe position equipment PE lwith the cord circuit CC and again bringingthe operator into telephonic communication with the calling mainexchangesubscriber.

In order to signal the subscriber at substation- B, the operatormomentarily actuates the common ring start-key K2, thereby applyingground potential to ring-start conductor 226, closingA a circuit throughcontacts of connect relay |06 for the lower winding of individualring-start relay |04. Ring-start relay |04 locks itself through itsupper winding by way of contacts of relays |03 and |02, and contacts ofthe key KI. At its upper and lower armatures, ring-start relay |04 opensthe talking strands and connects the ringing circuit through the plug LPto the called line. The tip conductor is now connected to theringing-current-supply conductor ||0', while the ring conductor isconnected through the winding of ring-trip relay |03 to the ungroundednegative pole of the exchange battery. Ringing current is now appliedintermittently in the usual manner to the line of substation B. Thecondenser |25, shunted around the upper armature and resting contact ofring-start relay |04, is of suicient size to permit a small amount ofringing current to pass back to the right-hand end of the cord circuitCC, serving as an indication both to the calling subscriber and to theoperator that the called subscriber is being signalled.

The operator is expected to restore her key KI as soon as she hasstarted the ringing operation and has heard the ringing-tone indicationabove mentioned. This brings about the restoration of connect relay |06and guard relay 20|.

When the subscriber at substation B responds to the applications ofringing current by removing his receiver, the direct-current bridgethereby closed across the conductors of his line results in theoperation of ring-trip relay |03. The locking circuit of ring-startrelay |04 is opened by relay |03, whereupon relay |04 restores therebyopening the ringing circuit and reclosing the talking strands of thecord. Answering-supervisory relay |05, whose lower winding is connectedin series with the lower talking conductor of the cord circuit CC, nowoperates over the line of substation B in series with line relay 404 inthe trunk circuit TC2 and in shunt of the supervisory-bridge resistor||4. At its inner upper armature, relay |05 closes a locking circuit foritself through contacts of key KI, and contacts of the operatedswitching relay |02. At its lower armature, relay |05 shunts its lowerwinding to provide a better talking circuit, while at its upper armatureit disconnects supervisory lamp |26. Answering supervisory relay |05opens the previously existing supervisory bridge through resistor ||4,.thereby placing line relay 404 of the trunk circuit TC2 under. thedirect control of the called line.

The two subscribers may now converse with each other as desired. I

Transfer service during an incoming' call In order to explain how thetransfer service operates during an incoming call, it will be assurnedthat the subscriber at substation B desires to obtain furtherinformation on some point under discussion before completing hisconversation with the calling main exchange subscriber. In this event.the subscriber at substation B momentarily operates his push button P2,thereby momentarily applying ground potential to one of the conductorsof his line to bring about a momentary unbalanced current fiow throughthe windings of the diierenital transfer-control relay 4| I. As aresult, transfer relay 4|0 is operated through its first step when thepush button PI is pushed and is operated through its second step whenpush button P2 is released. 'I'he line of substation B is thereupontransferred from the trunk T2 and over conductors 4|3-4I5 to the lineswitch LS4, which line switch operates in the usual manner to seize anidle selector such as SI. The subscriber at substation B now proceeds toset up the desired connection and obtain the desired information.

After the information has been obtained the local subscriber againoperates the push button Pl momentarily, whereupon transfer-controlrelay 4|| in the trunk circuit TC2 is again momentarily actuated. By theresulting operation of unlock relay 409 at this time, transfer relay 4|0is restored and relay 409 restores shortly thereafter. The connectionbetween the subscriber at substation B and the calling main exchangesubscriber is thus reestablished, while the line switch LS4 isdisconnected.

Transferring an incoming call to another local line In the event thatthe subscriber (at substation B) to whom the incoming call has beendirected decides that some other branch exchange subscriber (thesubscriber at A, for instance) should take over the call, he may signalthe branch exchange operator and request her to transfer the incomingcall.

In order to signal the branch exchange operator, the subscriber atsubstation B operates his calling device, preferably in accordance withsome digit greater than 5. As a result, a number of interruptions areproduced in the circuit of line relay 404 of the trunk circuit TG2. Eachtime its circuit is interrupted, relay 404 restores and applies groundpotential to conductor 426 but it does not interrupt the answeringbridge across the conductors of the trunk T2, for hold relay 408(operated because this is an incoming call) holds the bridge closed.Each time it applies ground potential to conductors 426, line relay 404closes a circuit through the sleeve of the trunk jack TJ and the sleeveof trunk plug TP for the supervisory and release-timer relay |08. Relay|08 operates the first time its circuit is closed. When it does so itcloses a local circuit for its upper winding, rendering itselfslow-releasing. Therefore, relay |08 is maintained operated throughoutthe dial-produced series of deenergizations of relay 404, by theslow-acting effect produced by the local circulating current in theupper winding of the relay. The somewhat momentary operation of relay|08 (during the transmission oi' the series of impulses) results in thecorresponding closure of a circuit for supervisory lamp |26 at armature|29. Lamp |26 therefore becomes lighted for a moment to attract theoperators attention.

The weighted spring |21 is struck by the associated armature, but thecontact produced by this action is an unsteady vibrating contact pref,erably for a period of substantially more than a second, with the resultthat the vibrating spring |21 does not come to rest (to thereby allowthe upper winding of relay |09 to become energized) during the somewhatmomentary interval that relay |08 is held operated responsive to thesucceeding impulses of the recall series. Relay |09 is somewhat slow tooperate, as indicated, for which reason it does not respond in any eventto the operation of relay |08 until the vibration of the weighted spring|21 has substantially ceased.

When relay |08 restores, upon the cessation of the impulses, lamp |26becomes extinguished.

The above signalling operation may be repeated as often as desired, oruntil the operator responds.

The operator responds to the above lighting of supervisory lamp |26 bythrowing her key KI to talking position, bringing about the reoperationof connect relay |06 and guard relay 20|. The operator may converse withthe local subscriber and discover to whom the call should betransferred, which transfer operation is carried out by removing theplug LP from the local jack and by proceeding to make connection withthe line of substation A through jack LJ l. When the plug LP is removedfrom the jack LJ2, idle-test relay switching relay |02, and answeringsupervisory relay restore successively, placing the cord circuit incondition for making a new connection. Line relay 404 is held operated,during the transfer of the plug LP, through the oper- Aators headsetconductors, and resistor H4 is Clearing out the incoming connection Whenthe inter-exchange conversation is completed, the calling main exchangesubscriber and the local branch-exchange subscriber replace theirreceivers. When thereceiver is replaced at substation A, line relay 404in the trunk circuit TC2 restores and opens the circuit of release relay405, permitting relay 405 to restore after a slight interval. Hold relay408 is unlocked by release relay 405. Disconnect supervision is given tothe main exchange at the upper contacts of hold relay 408. With releaserelay 405 restored, conductor 423 is ungrounded to mark the trunk T2idle at the selectors such as SI.

Line relay 404 also applies ground potential to sleeve conductor 426,thereby closing a circuit through the sleeve of the jack TJ of the plugTP for supervisory relay |08. Relay |00 operates and at armature |29closes a circuit for supervisory inner upper armature of switching relay|02, and' contacts of key KI. Cut-oil? relay |09 is therefore operatedafter an interval of somewhat more than one second has elapsed, duringwhich interval the weighted spring of contact |21 goes through itsperiod -of vibration. Upon operating, relay |09 locks its lower windingto the sleeve of the plug PT, at the same time opening the talkingstrands of the plug TP. At contacts controlled by the middle lowerarmature, relay |09 removes'ground potential from one terminal ofidle-test relay |0| thereby freeing the line of substation B andpermitting idle-test relay |0| and switching relay |02 to restore. Atits upper armature, switching relay |02 opens the initial circuit ofcut-oi relay |09, but cut-off relay |09 is now maintained operated inthe locking circuit including its lower winding and the sleeve conductorof the plug and jack. Answering supervisory relay |05 is also restoredby the opening of the inner upper contacts of relay |02.

Answering supervisory relay |05, at its lower armature, again bridgesthe resistor ||4 across the strands of the cord circuit CC, but'thisdoes not result in a reoperation of line relay I 04 of the trunk circuitTG2, because the tip and ring conductors of the trunk plug TP aredisconnected at contacts of cut-oli relay |09.

It is to be particularly noted that both the line of substation B andthe trunk circuit TCZ are freed for furtherA use, even though theoperator permits the plugs LP and TP of the cord circuit CC to remain inthe jacks LJ 2 and TJ indefinitely.

When the operator removes the plugs LP and TP, relays |00 and |09 in thecord circuit CC restore, returning the cord circuit to normal condition,supervisory lamp |26 being extinguished at armature |29 of relay |08.

In the event that the trunk line T2 is seized at the automaticswitchboard in an outgoing call while the plug TP is still in the trunkjack TJ, and the local plug LP is still in the local jack LJ2,jack-cut-off relay 4| 2, upon operating in series with conductor 42|upon the seizure of trunk circuit TC2, places ground potential directlyon conductor 426 at its lower armature so as to maintain relay |09 ofthe cord circuit CC actuated' after line relay 404 has operatedresponsive to the seizure.

Conductor 426 is thus maintained grounded at jack-cut-ofi relay 4 2 forthe duration of the outgoing call, and ground potential is reapplied tothis conductor by line relay 404 at the termination of the call beforejack-cut-oi relay M2 is permitted to restore.

In the event that an incoming call is received over the two-way trunk T2while the trunk plug TP still is in the trunk jack TJ and the local plugLP is still in a local jack, the call lamp |24 at the jack TJ is lightedin the usual manner over conductor 428 when call relay 401 responds tothe actuation of ring-up relay 406. Upon noting the lighted condition ofthe call lamp |24, the operator iirst removes the local plug LP from thelocal jack and then momentarily removes the trunk plug TP from the trunkjack TJ, again inserting the plug in the jack. The momentary removal ofthe trunk plug TP from the jack TJ, permits relays |08 and |09 torestore, and relay |09 is thus permitted to again connect up the talkingconductors of the plug TP to the cord. TherelOering an incoming call toan idle line Since the VcordCC is a dry cord`(it contains nocurrent-supply bridge) special arrangements must be made to furnishtalking current to the called local line in the event that the operatordesires to converse with thelocal called sub- -scriber without theknowledge of the calling main exchange subscriber, ordinarily for thepurposeo-determining whether or not the tentatively selected localsubscriber is the one to take the call.

1n order to spia the cord cc, the operator (with the talking key K! andconnecting relay |06 in the cord operated, together with guard relay 20|of position equipment PE) operates the common key K2 to split position,in which position the left-hand contacts of the key are actuated. The

` lower contacts 'of the split key place ground potential on splitconductor 228, closing a circuit through contacts of operated relay |06for split relayf |01 in the cord circuit. Relay |01 bridges the dialconductors 229 and 230 across the tip and ring conductors of the trunkplug TP, to hold the line relay of the connected trunk in operatedcondition. At the same time, the talking strands of the cord circuit areseparated at the contacts of relay |01, whereby the telephonieconnection with the calling main-exchange line is severed.

The local line reached through the plug LP ls now deprived of itsprevious supply of energizing current for the transmitter. Therefore inthe position equipment PE contacts of the split key K2 operate the feedrelay 203 to connect the retard bridge 204 across the operators tip andring conductors 220 and 223 `as a transmittersupply bridge for the localline, at the same time inserting condensers between conductors 223 and220 and the operators telephone equipment, it

being unnecessary to send transmitter current through the secondarywinding of the induction l The operator now proceeds to converse withthe local subscriber and determine whether or not he is the one to takethe incoming call. It is to be noted that the upper contactsof the splitkey K|2 disconnect the upper winding of tone relay 202 from toneconductor 225, so that this tone relay is not operated at this time toplace a warning tone on the operators headset conductors and theconductors of 'the called local line. This warning tone is obviouslyunnecessary now, as the conversation is Vonly between the operator andthe local subscriber.I

Assuming that the called local subscriber is the one to take the call,the operator restores the talking key Kl ,and split key K2. Feed relay203 in the position equipment PE restores, as does split relay |01 inthe cord circuit CC. e

The twosubscribers may now converse through the cord circuit CC.

Putting through a delayed cazz The way in which a delayed outgoing callis handled by the branch exchange operator will now be explained. Forthis'purpose it will be assumed that the subscriber at substation A,being unable to ,reach a desired main exchange subscriber, requests theswitchboard operator to make an attemptto set up the connection for him,such a call being termed a delayed call. To complete the delayed call,the branch exchange opthe trunk plug TP of the cord circuit CC, forexample, into a trunk jack, such as TJ, associated with a two-way trunkwhich is idle, the

busy or idle condition being indicated by the lighted or unlightedcondition of the busy lamp erator inserts. the trunk plug o( an idlecord,

as previously pointed out, in series with resistor l I4 bridged acrossthe strands of the cord circuit CC. Releasel relayr 405 applies groundpotential to conductor 423 to guard the trunk circuit TG2 againstseizure at the automatic switchboard. At its upper contacts line relay404 closes a bridge across the conductors of the trunk T2 through theleft-hand windings of repeating coil 403 and resistor 413, therebysignalling the main -exchange operator in the event the main exchange isa manual exchange, or taking a first selector for usein the mainexchange in the event that it is an automatic exchange. The throwing ofthe key KI into talking position associates the position equipment PEwith the cord circuit CC, so that the branch exchange operator mayconverse with themain exchange operator and request the number shewants. f

Setting up the delayed connection when the main exchange is an automaticexchange For the purpose of explaining the dialling feature oi' theposition equipment PE, the cord circuit CC, and the trunk circuit TC2,it will be assumed now that the main exchange is an automatic exchange,in which event the operator must control the transmission of diallingimpulses to bring about the setting of the automatic switching apparatuson the terminals of the desired main exchange line.

With the key KI operated in CC, the operator actuates the key K2, Fig.2, to split position, thereby placing ground potential on splitconductor 228. As a result split relay |01 in the cord circuit CC isoperated through contacts of connect relay |06. In addition todisconnecting the lower winding of supervisory relay |08, relay |01connects dial-tip and dial-ring conductors 229 and 230 to the tip andring conductors of the trunk plug TP, at the same time disconnecting thetwo p lugs of the cord from each other to prevent dialling interferencefrom the local plug in the event that the operator has already madeconnection to' the 'local line. The line relay 404 of the connectedtrunk circuit TC2 is now held operated over the dial-,tip and dialringconductors 229 and 230, through contacts of the actuated split relay|01, resistor 235 in the position equipment PE,'.and impulse contacts232 of the calling device 23|.

When the operator actuates the dial (not shown) of the vcalling device23| from its normal position pursuant to the dialling of the firstdigit, off-normal contacts 233 and 234 close. Oil-normal contacts 233shunt the associated resistor 235 so as to form a better dialling"circuit for relay 404 in the trunk circuit TC2, while cifnormal contacts234 apply ground potential at a ,second point to split conductor 228, soas to inthe cord circuit variably maintain the split relay |01 operateduntil the calling device reaches normal position. This' latter featureis of utility in the event that the operator, upon the dialling of thefinal digit, restores her split key before the calling device completesthe transmission o f the nal digit.

As the calling device 23| returns to normal, the impulses aretransmitted by the predetermined number of momentary separations ofimpulse contacts 232, which contacts are shuntedl by the usual sparksuppressor condenser and associated resistor, as shown.

After she has completed dialling the desired umber, the operatorrestores the key K2, bringing about the restoration of split relay |01to ter# minate the split condition of the cord circuit CC.

Assuming now that the desired main exchange subscriber responds, theoperator may request him to wait a moment while she gets in touch withthe subscriber at substation A. 'I'his she does by inserting the localplug! LP ,in the line jack LJ2 and momentarily operating the ringstartkey K2 to bring about the operation of ringstart relay |04. Relays |0|and |02 operate responsive to the insertion of the plug LP'into the jackLJ 2 to prepare the talking circuit, while the ring-start relay |04starts the operation. From this point the operations are ashereinbei'ore described.

Night service In order to provide for the reception of calls incoming tothe branch exchange by such subscribers as are on duty at night or atother times when the branch-exchange switchboard is unattended,the trunkT2 may be extended directly to a branch-exchange line, the lineofsubstation B, for example. This extension is made through a cordcircuit, the cord circuit CC,'for example. In this event, the key KI isactuated to night position and the trunk plug TP is inserted into thenight jack NJ, Fig. 4, while the local plug LP is inserted into the jackLJ2.

The upper contacts of jack NJ ground conductor 423 to guard thetrunk-against seizure at the automatic switchboard. With the plug LP injack LJ2, idle test and switching relays I 0| and |02 are actuated, asin a standard call to the local line. Moreover, answering supervisoryrelay |05 is held continuously operated at contacts of the night' kewhereby the resistor I|4 isl not in bridge of the talking strands of thecord, andlamp |26 is maintained extinguished.

Henceforth, each time an incoming call is received over trunk T2,ringing current passes through jacks NJ and LJ2 by way of cord circuitCC to the line of substation B. such incoming calls, therefore, may beanswered directly at B. Moreover, when h e desires to do so, thesubseriber at B may make an outgoing call directly over the trunk T2,which has been rendered individual to his line as above described.

When desired, the operator may inform the subscriber at substation Bwhen his line is about to be converted to' thenight condition. For thispurpose, before placing the plug 'I'P into the jack NJ, the operatorplaces the plug LP into the jack LJ 2; operates the talking key;momentarily operates common key K2 to ring-start position to start theringing operation and then operates K2' to split position to cause feedrelay 20.3 vto operate and connect up retard 204 as a transmitter-supplybridge foruse when the called subscriber responds.

After the subscriber responds and acknowledges the information, theoperator restores K2; actuates Kl to night position; and inserts plug LPinto night jack N 'Ihe upper contacts of the night section of key KIopen the lockingcircuit of ring-start relay |04 to restore this relay inthe event that the subscriber at substation B does not. respond, whilethe middle contacts of the key separate the circuits of relays |05 and|04 to prevent the operating potential applied to the upper winding ofrelay |05 lfrom driving a holding current through relay |05.

What is claimed is:

1. In a telephone system, lineswitches terminating subscriber lines,respectively, other lineswitches, links accessible to all saidlineswitches, means responsive to the removal of the receiver on asubscriber line'for operating the associated lineswitch to take one ofthe links for use, means for extending a connection from the seized linkto a desired called line, a transfer link included in the extendedconnection or not depending upon the line called, one of said otherlineswitches being individual to said' transfer link, and meanscontrolled at will over the line of the calling subscriber in the event-that the extended connection includes said transfer link for severingthe distant end of the transfer link and for operating the associatedlineswitch to extend the calling line by way of the near end of thetransfer link and the associated individual lineswitch to another one ofthe first named links.

2. In a telephone system, lineswitches terminating subscriber lines,respectively, other lineswitches, links accessible to all saidlineswitches, means responsive to the removal of the receiver on asubscriber link for operating the associated lineswitch to take one ofthe links for use, means for extending a connection from the seized'link to a desired called line, a transferlink included in the extendedconnection or not depending upon the line called, one of said otherlineswitches being individual to said transfer link, means controlled atwill over the line of the calling subscriber in the event that theextended I connection includes said transfer link for severing thedistant end of the transfer link and for operating the associatedlineswitch to extend the calling line by way of the near end of thetransfer link and the associated individual lineswitch to another one ofthe first named links, and means subsequently controlled at the will ofthe calling subscriber for freeing the link taken for use by way of thelast-named lineswitch and for reconnecting the severed portion of thetransfer link.

3. In a telephone system, two groups of serially related link circuitsfor use in setting up telephone connections betweenl subscriber lines, agroup of subscriber lines, each line extending to a lineswitch havingaccess'to links of the rst vgroup, switching apparatus for extending aseized link of the rst group to a link of the second group, each linkyof the second group having a normally connected branch and a normallydisconnected branch, each of said normally disconnected branchesextending to a lineswitch having access to links of the first group, andmeans controlled at will over the line of a calling subscriber when aconnection has been set up therefore through one of the links of thesecond group for disconnecting the normally connected branch and forconnecting the normally disconnected branch to cause the `associ-- atedlineswitch to operate and extend the calling line to a second link inthe rst group.

4. In' a telephone system, a trunk line extend- 1 ing from a rstexchange 'to a second exchange,

to said trunk line by way of the first branch, an

automatic switch terminating the second branch, andmeans controlled atwill over the subscriber line for substituting the second branch for thetrunk line to extend the subscriber line to said automatic switch andsubsequently controlled at will over the calling line for substitutingthe trunk line for the said second branch.

5. In a telephone system, a trunk line extending from a first exchangeto a second exchange. said trunk line having rst, second, and thirdbranches in the iirst exchange, switching means in the rst exchange forconnecting a subscriber -line with the trunk line by way of the iirstbranch, switching means for connecting a subscriber line with the trunkline by way of the second branch, an automatic switch terminating thefirst branch and means controlled at the will of the subscriber on aline connected with the trunk line by way of either the first branch orthe second branch for substituting the third branch forthe trunk line toconnect such subscriber line with the automatic switch, and subsequentlycontrolled at will for substituting the trunk line for the said thirdbranch.

6.. In a telephonesystem, a trunk line having a first branch and asecond branch at one end thereof, means for connecting a subscriber linewith said trunk line by way of the first of said branches, a supplybridgeV in said trunk line for supplying transmitter current to theconnected subscriber line, a differential control relay in the iirstbranch non-responsive to the normal balanced ow of current over thesubscriber line, means at the substation on the subscriber line fortemporarily unbalancing the flow of transmitter current to bring aboutan operation of said control relay, means responsive thereto forsubstituting the second branch for the said trunk line,

. means in the second branch for supplying a ow of transmitter current,and means responsive to a further operation of said control relay in theevent that the ilow of transmitter current therethrough from the secondbranch is subsequently unbalanced at the station on the subscriber linefor substituting the trunk line for the said second branch.

Ameans controllable by the '7. In a branch telephone exchangetrunk-connected with a main exchange, an automatic switchboard and amanual switchboard, means at the automatic switchboard connections andfor setting up connections to the main exchange by way of the trunklines, means at the manual switchboard for completing incomingconnections from the trunk lines 'to the local lines, meanseiective inthe event of a connection incoming from the main exchange or of 'aconnection outgoing to the main exchange for enabling the localsubscriber at will to transfer the connection temporarily from the mainexchange to another local line, and subsequently back to the mainexchange again, and operatorl through lthe manual switchboard responsiveto a signal from the local subscriber for transferring an incomforcompleting local interconnecting 1 ing connection from the local lineoriginally connected with to a desired other local line.

8. In a combined automatic and manual branch exchange trunk-connected tothe main exchange, means including a cord circuit at the manualswitchboard for interconnecting an incoming trunk line with a local lineto complete an incoming connection, a transfer relay in the trunk line,a supervisory relay and a cut-off relay in the cord circuit, and meansselectively controlled over the called line for actuating the saidrelays.

9. In a branch exchange trunk-connected with` a main exchange throughtwo-way 'trunk lines, an automatic switchboard through which localconnections may be made and connections through which outgoing to themain exchange over said trunk lines may be made, a manual switchboard,an extension from each two-way including a double-plug cord circuit atthe many ual switchboard for interconnecting a subscriber line with atrunk line, and means automatically eective when the subscriber on theinterconnected line replaces his receiver after the termination of aconversation for disconnecting both plugs of said cord circuit tothereby free the subscriber lineior further use and to free the trunkline for further use while the plugs of the cord circuit remain inplace.

11. In a telephone system, a manual switchboard having cord circ 'tsthrough which desired connections are extended, the talking strands ofthe calling plug of each cord circuit being normally open, meansdependent upon the called line being in an idle condition for closingthe calling strands of the cord circuit, and means including an offeringcord and plug forming an extension of the operator's headset conductorsfor enabling the operator to make connection with a busy line to oier acall.

12. In a telephone system, a plug ending cord having the tip and ringconductors normally open, a busy-test relay normally connected to thetip of the plug, and relay apparatus operable over the sleeve of a 'jackinto which the plug is inserted for disconnecting the busy-test relayand for closing the tip and ring conductors, depending upon an idlecondition of the line associated with the said jack.

13. In a telephone system, a plug ending cord having the tip and ringconductors normally open, a busy-test relay normally connected to thetip of thel plug, relay apparatus operable over the sleeve of a jackinto which the plug is inserted for disconnecting the busy-test relayand for closing the tip and ring conductors, depending upon an idlecondition of the line associated with the said jack, and meanscontrolled by the busytest relay when the line associated'with the jackwith which the plug is brought into engagement is busy for placing abusy-tone potential on the cord.

14. In a combined automatic and manual branch exchange trunk-connectedto the main exchange by two-way trunks appearing both at the automaticswitchboard and at the manual when the operator plugs into one of saidlines and when she plugs into one of said trunks for preventingintrusion upon a busy connection if one is taking place and forpreventing interference with the transmission of switch settlingimpulses in the event that an automatic connection is being 'set up.

JOHN H. VOSS.

